1. Field of the Invention
This invention relates to an optical switch array, and in particular, to such an optical switch array utilizing the temperature dependent characteristics of the index of refraction of a dielectric crystalline material.
2. Description of the Prior Art
In optically modulating apparatuses, optical shutters, applied instruments thereof, and electrophotographic copiers and printers, it is required to provide a device for optically recording image information at high speed. As an example of such a device, an optical switch array including a plurality of optical switches which are arranged in the form of a single array and selectively operated to be on or off in accordance with an electrical image signal supplied thereto is well known. The prior art optical switch arrays utilize either the magnetooptic effect or the electrooptic effect in carrying out the switching operation. For example, in the former case, use is typically made of a single crystal or epitaxial film of Gd.sub.3-x Bi.sub.x Fe.sub.5-x Ga.sub.y O.sub.12 and the on/off control of light is effected by utilizing the magnetooptic effect of such a single crystal or thin film. On the other hand, in the latter case, use is typically made of a ceramic material of PLZT having a crystalline structure expressed by (Pb.sub.1-x La.sub.x)(Zr.sub.1-y Ti.sub.y).sub.1-x/4 O.sub.3 and its secondary electrooptic effect, so-called Kerr effect, is utilized to carry out the on/off control of light as disclosed in the Japanese Patent Laid-open Publication No. 52-8842.
However, in the case where the magnetooptic effect is to be used, it is laborious to manufacture a single crystal or thin film of Gd.sub.3-x Bi.sub.x Fe.sub.5-x Ga.sub.y O.sub.12 and thus difficulty is encountered if it is desired to make such a crystal or film having a larger area. Further, in order to carry out switching operation, it is necessary to increase the temperature above the compensated temperature by 20.degree. to 30.degree. C. and to apply a magnetic field having the strength of approximately 100 ersteds. It is also necessary to provide input and output polarizers which will decrease light intensity and cause complication in overall device structure.
In the case where the electrooptic effect is to be used, there also exists difficulty in making a larger-sized optical switch array because there is a limit in size in manufacturing a PLZT crystal and the largest size of such a crystal is typically a few centimeters by a few centimeters at most. Moreover, electrodes to be used are complicated in structure and thus manufacture thereof is difficult. Further, a relatively high driving voltage ranging from 80 to 250 volts is required. It should also be noted that provision of input and output polarizers is required similarly with the magnetooptic case.